WASHINGTON (CNN) -- President Bush gave an upbeat assessment Thursday of security strides in Iraq as U.S. troop deaths headed for their lowest monthly total since early in the war.

President Bush on Thursday said progress in Iraq will allow shorter tours of duty, starting Friday.

"Violence is down to its lowest level since the spring of 2004, and we're now in our third consecutive month with reduced violence levels holding steady," Bush said.

Troop reductions this year could continue if security holds, he said, and he announced that Army troops newly deployed to Iraq would serve 12 months instead of 15, starting Friday.

The deployment decision, which applies to new soldiers heading to Iraq, was first announced in April.

Defense Secretary Robert Gates said separately Thursday that conditions in Iraq have improved "dramatically."

"There is a real possibility of some additional drawdowns as we look forward," Gates told reporters.

The new tour policy "relieves the burden on our forces, and it will make life easier for our wonderful military families," Bush said during brief remarks at the White House. Watch how Bush assesses situation in Iraq »

Tours will not be reduced for currently deployed troops.

Bush said there's a "degree of durability" to the gains made in reducing violence in Iraq. He credited last year's increase in U.S. troop strength and the rising competency of Iraqi security forces.

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A CNN-Opinion Research Corp. poll of 1,041 adults conducted on July 27-29 found 62 percent favor a timetable for withdrawing U.S. troops from Iraq, while 37 percent oppose setting deadlines. The results had a margin of error of plus or minus 3 percentage points.

The same poll found 52 percent consider the troop surge a success and 41 percent consider it a failure. The error margin on that question was plus or minus 4.5 percentage points.

Overall, 37 percent think the United States is winning the war in Iraq, 6 percent think the insurgents are winning, and a majority, 57 percent, say no one is winning. That question also had a 4.5 percent error margin.

Sixty-six percent of those polled oppose the war in Iraq, while 33 percent favor it. The war in Afghanistan is opposed by 52 percent, but 56 percent say troop levels there should be increased as levels in Iraq are reduced.

The margin of error on those questions was 3 percentage points.

The president Thursday praised Iraqi forces for purging Shiite extremists from Basra, Amarra and Baghdad's Sadr City neighborhood.

As a result of these successes, U.S. Ambassador Ryan Crocker was able to walk through Sadr City last week, he said.

"That's something that would not have been possible just a few months ago," Bush said.

He also noted political progress in Iraq, as the Parliament has advanced legislation and Prime Minister Nuri al-Maliki recently completed a diplomatic trip to Europe.

Ten U.S. troop deaths have been reported this month. Four were killed in hostilities and six died from nonbattle-related causes, according to the Pentagon.

Two other soldiers who have been missing since May 2007 were found dead this month, but it is not known when they died.

The lowest monthly toll had been in May, when 19 were killed.

U.S. casualties have been lower in 2008 than last year. There were 40 deaths in January, 29 in February, 38 in March, 52 in April, 19 in May, and 29 in June.

Last year, there were 83 deaths in January, 81 in February, 81 in March, 104 in April, 128 in May, 101 in June, 80 in July, 84 in August, 65 in September, 38 in October, 37 in November, and 23 in December.

"We now have brought home all five of the combat brigades and the three Marine units that were sent to Iraq as part of the surge. The last of these surge brigades return home this month," Bush said.

The number of monthly Iraqi civilian deaths in Iraq also is declining, according to the Iraqi government. In July, 387 Iraqi civilians were killed in conflict-related violence, compared with 448 in June and 504 in May.

However, the number of Iraqi police and soldier casualties in July was higher than June's figure.

In July, 45 Iraqi police officers were killed and 83 were wounded. In June, 41 police were killed and 110 were wounded.

Thirty-three Iraqi soldiers were killed and 63 were wounded in July. In June, 21 soldiers were killed and 47 were wounded.

Bush said later in the year, Gen. David Petraeus, the top U.S. commander in Iraq, will provide "recommendations on future troop levels, including further reductions in our combat forces as conditions permit."

Still, "we remain a nation at war," Bush said. "Al Qaeda is on the run in Iraq, but the terrorists remain dangerous and they are determined to strike our country and our allies again."

Bush said the United States is "making progress" in its discussions with Iraq "on a strategic framework agreement," which would "serve as the foundation for America's presence in Iraq" once a U.N. mandate authorizing multinational forces expires at the end of the year.

The administration had hoped to forge an agreement by the end of July but both sides continue to negotiate.